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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 27 (1997), S. 327-355 
    ISSN: 1573-1634
    Schlagwort(e): surface tension ; porous media ; Marangoni–Bénard ; instability.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract The Rayleigh–Bénard instability for a clear fluid has its equivalent for a liquid saturated porous matrix. The phenomenological Darcy momentum law cannot give rise by itself to an instability analogous to that of Bénard–Marangoni, but the Brinkman model at least allows it. A critical Marangoni number exists leading to cellullar patterns and, for realistic values of the permeability, it is proportional to the inverse of this last parameter.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 34 (1999), S. 117-128 
    ISSN: 1573-1634
    Schlagwort(e): porous media ; Biot's theory ; nonlinear waves ; asymptotic methods ; evolutionary equations.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract Nonlinear wave dynamics of an elastically deformed saturated porous media is investigated following the Biot approach. Mathematical models under research are the Biot model and its generalization by consideration of viscous stresses inside liquids. Using two-scales and linear WKB methods, the classical Biot system is transformed to a first-order wave equation. To construct the solution of the other system, an asymptotic modified two-scales method is developed. Initial system of equations is transformed to a nonlinear generalized Korteweg–de Vries–Burgers equation for quick elastic wave. Distinctions of wave propagation in the context of the Biot model and its generalization are shown.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 25 (1996), S. 235-246 
    ISSN: 1573-1634
    Schlagwort(e): experiment ; porous media ; periodic heterogeneity ; characteristic length scale ; scale-dependent dispersion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract An experimental investigation of scale-dependent dispersion in periodic heterogeneous porous media was conducted. Models with two-, three- and four-layer periodic heterogeneities were constructed to investigate the effect of heterogeneity size on the scale-dependence of dispersion. Longitudinal dispersion coefficients were determined as a function of column length by measuring the breakthrough of a continuous injection of potassium chloride tracer solution. Chloride ion concentration was monitored by recording the millivolt potential of silver/silver chloride electrodes placed at intervals along the length of the column. In all three models, dispersion appeared to be scale dependent up to a distance of approximately 20–30 times the size of the repeated heterogeneity group (hydraulic unit). Because all three models suggested a similar dependence, it was concluded that a medium with periodic heterogeneity may likely be characterized by the scale of its hydraulic unit.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 33 (1998), S. 279-293 
    ISSN: 1573-1634
    Schlagwort(e): surface reactions ; critical points ; convective flow ; porous media ; Darcy flow
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract A model for the convective flow in a fluid‐saturated porous medium containing a reactive component is considered. This component undergoes an exothermic reaction (modelled by a first order mechanism) on an impermeable bounding surface, the resulting heat released driving the convective flow. Large Rayleigh number flow near a stagnation point is treated in detail by first considering the steady states. Multiple solution branches and critical points arising from a hysteresis bifurcation are identified. The form that these solution branches take depends on whether or not the effects of reactant consumption are included. An initial‐value problem is then discussed. This shows that both the lower (slow reaction) and upper (fast reaction) solution branches are stable (and the ultimate state of the system). When the parameter values are such that there is no steady state, the solution develops a finite‐time singularity, the nature of which is analysed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 34 (1999), S. 101-115 
    ISSN: 1573-1634
    Schlagwort(e): porous media ; macro-and microscopic approches ; compressible and incompressible incompressible fluid ; incompressible fluid ; effective stress concept.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract In this paper two complementary approaches are used to describe the mechanical behavior of saturated compressible and incompressible porous solids. The macroscopic investigation is based on the mixture theory, restricted by the volume fraction concept. In the micromechanical approach, a hierarchy of conditionally ensemble averaged fluid and solid phase momentum balance equations are derived for a simple model of quasi-static liquid saturated porous media. The ensemble averaged equations for both the phases agree remarkably well with the macroscopic results. A micromechanical basis for Terzhagi's effective stress concept is presented. In addition, an expression for additional partial solid stress modifying the effective stress principle, to account for deformability of solid materials, is also derived.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 21 (1995), S. 101-122 
    ISSN: 1573-1634
    Schlagwort(e): discretization scheme ; numerical heat transfer ; porous media
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract A new numerical scheme, theimplicit correction scheme, has been developed for heat transfer in a porous medium with strong temperature gradients. The scheme includes diffusion, convection and transverse heat transfer processes. By using correction coefficients which are based on transverse heat transfer, the effects of convection enthalpy flow and diffusion are modified. Under suitable limiting conditions, the implicit correction scheme can be reduced to the central-difference, upwind, or power-law scheme. The correction scheme is shown to be especially useful in calculations of the thermal effectiveness of the regenerator in Stirling cycle refrigeration.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    ISSN: 1573-9686
    Schlagwort(e): Biomechanics ; Constitutive behavior ; Cardiac mechanics ; Myocardium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Finite extension and torsion tests on cardiac papillary muscles are presently the best way to directly measure the response to shear along myocardial fibers. Quantifying this response is necessary for determining the complete three-dimensional constitutive behavior of myocardium as a transversely isotropic material. Analysis of such tests is complicated, however, since papillary muscles are materially inhomogeneous, consisting of a myocardial core surrounded by an endocardial sheath that is rich in collagen. In this article, we show that the papillary muscle response to extension and torsion additively decouples into the response of the bare myocardial core plus the response of an endocardial sheath filled with fluid (assuming the muscle is a radially inhomogeneous and incompressible continuum with cylindrical symmetry). This result allows the endocardial response to be subtracted from the intact papillary muscle response to obtain the response of the bare myocardial core. An initial estimate suggests that the endocardial sheath affects the axial moment significantly (50% of torque for all twists at low stretch) but affects the axial force only slightly (〈10% at moderate twists). © 1999 Biomedical Engineering Society. PAC99: 8719Hh, 8719Rr, 8719Ff
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Annals of biomedical engineering 27 (1999), S. 721-730 
    ISSN: 1573-9686
    Schlagwort(e): Fibroblast ; Cornea ; Biomechanics ; Collagen matrix ; Finite-element modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Although it is known that cells promote structural reorganization of the collagen architecture, how individual cells exert mechanical tension on the matrix is not clearly understood. In the present study we have investigated the mechanical interaction of individual corneal fibroblasts with a collagen matrix using an improved version of our previously described in vitro force-measurement system (Roy, P. et al. Exp. Cell Res. 232:106–117, 1997). The elastic distortion of the collagen matrix exerted by cells was temporally recorded and analyzed using a two-dimensional finite-element model to quantify the forces exerted on the matrix. Time-lapse videomicroscopy of serum-cultured cells on the matrix for up to 6 h revealed that individual fibroblasts generated measurable tension on the matrix during pseudopodial extension and slow retraction. Fast retraction, an event observed during active cell migration, was associated with dramatic release of tension on the matrix. An apparent inverse correlation was observed between cell translocation and maintenance of matrix tension. Additional experiments with cells under serum-free conditions revealed that these cells fail to generate any detectable tension on the matrix despite undergoing filopodial extension and retraction. Since serum-free cells do not form focal adhesions or stress fibers, these experimental data suggest that contractility of nonmotile cells, coupled with strong cell–matrix adhesion, is the most favorable mechanism of generating and maintaining tension on the extracellular matrix. © 1999 Biomedical Engineering Society. PAC99: 8718Ed, 8715La, 8714Ee, 4266Ct, 0270Dh
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Annals of biomedical engineering 27 (1999), S. 805-814 
    ISSN: 1573-9686
    Schlagwort(e): Rehabilitation ; Neurological control systems ; Bioinstrumentation ; Biomechanics ; Spasticity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract We report the use of a mechatronic device for assessing arm movement impairment after chronic brain injury. The device, called the “Assisted Rehabilitation and Measurement Guide,” is designed to guide reaching movements across the workspace, to measure movement and force generation, and to apply controlled forces to the arm along linear reaching paths. We performed a series of experiments using the device in order to identify the contribution of active muscle and passive tissue restraint to decreased active range of motion of guided reaching (i.e., “workspace deficits”) in a group of five chronic, spastic hemiparetic, brain-injured subjects. Our findings were that passive tissue restraint was increased in the spastic arms, as compared to the contralateral, nonparetic arms. Active muscle restraint, on the other hand, was typically comparable in the two arms, as quantified by measurements of active arm stiffness at the workspace boundary during reaching. In all subjects, there was evidence of movement-generated weakness, consistent with a small contribution of spasticity to workspace deficits. These results demonstrate the feasibility of mechatronic assessment of the causes of decreased functional movement, and could provide a basis for enhanced treatment planning and monitoring following brain injury. © 1999 Biomedical Engineering Society. PAC99: 8719La, 8719St, 8780Vt, 8719Nn, 8719Ff
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    ISSN: 1573-9686
    Schlagwort(e): Spasticity ; Stretch reflex ; Biomechanics ; Stroke ; Hemiparesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract A parametric model of the human reflex torque response to a large-amplitude, constant angular velocity elbow extension was developed in order to help quantify spasticity in hemiparetic stroke patients, and to better understand its pathophysiology. The model accounted for the routinely observed leveling of torque (i.e., a plateau) at a mean angular increment of 51°±10° s.d. (n=98) after the initial rise. This torque “plateau” was observed in all eight subjects, and in 98 of 125 trials across 25 experimental sessions. The occurrence of this plateau cannot be explained by decreases in elbow flexor moment arms during elbow extension. Rather, the plateau is attributable to a consistent leveling in muscle activation as confirmed both qualitatively from recordings of rectified, smoothed electromyograph (EMG) activity, and quantitatively using an EMG coefficient model. A parametric model was developed in which the pattern of muscle activation in the stretch reflex response of elbow flexors was described as a cumulative normal distribution with respect to joint angle. Two activation functions, one related to biceps and the other to brachioradialis/brachialis, were incorporated into the model in order to account for observations of a bimodal angular stiffness profile. The resulting model yielded biologically plausible parameters of the stretch reflex response which may prove useful for quantifying spasticity. In addition, the model parameters had clear pathophysiological analogs, which may help us understand the nature of the stretch reflex response in spastic muscles. © 1999 Biomedical Engineering Society. PAC99: 8719Rr, 8719Xx, 8719St, 8719Nn, 8719Ff, 8710+e
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 18 (1995), S. 1-13 
    ISSN: 1573-1634
    Schlagwort(e): Mixed convection ; thermal plume ; line source ; porous media
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract A boundary-layer analysis is presented for the mixed convection flow which is produced when a horizontal line heat source, which is embedded in an infinite fluid-saturated porous medium, generates heat at a constant rate. It is shown that the governing equations can be non-dimensionalized so that they do not involve any parameters and thus just one solution of the transformed boundary-layer equations is required. Series solutions which are valid both near the line source and far downstream are obtained and compared with the numerical solution of the full boundary-layer equations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 28 (1997), S. 285-306 
    ISSN: 1573-1634
    Schlagwort(e): fissured media ; homogenization ; dual porosity ; modeling ; microstructure ; porous media
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract Totally fissured media in which the individual cells are isolated by the fissure system are effectively described by double porosity models with microstructure. Such models contain the geometry of the individual cells in the medium and the flux across their interface with the fissure system which surrounds them. We extend these results to a dual-permeability model which accounts for the secondary flux arising from direct cell-to-cell diffusion within the solid matrix. Homogenization techniques are used to construct a new macroscopic model for the flow of a single phase compressible fluid through a partially fissured medium from an exact but highly singular microscopic model, and it is shown that this macroscopic model is mathematically well posed. Preliminary numerical experiments illustrate differences in the behaviour of solutions to the partially fissured from that of the totally fissured case.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 25 (1996), S. 275-282 
    ISSN: 1573-1634
    Schlagwort(e): combined convection ; porous media ; heat transfer ; thermal stratification ; thermal dispersion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract The effects of thermal dispersion and thermal stratification on mixed convection about a vertical surface in a porous medium are studied. The conservation equations that govern the problem are reduced to a system of nonlinear ordinary differential equations. The resulting equations are solved on the basis of the local similarity approximation. The results indicate that both dispersion and stratification effects have considerable influence on the heat transfer rate.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 36 (1999), S. 245-254 
    ISSN: 1573-1634
    Schlagwort(e): porous media ; heat transfer ; mixed convection.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract In the present work, the effect of mixed convection about vertical surfaces on the phenomenon of melting process in a fluid-saturated porous medium is analyzed on the basis of boundary layer approximations. Similarity solutions are obtained for aiding external flow. The final similarity equations are integrated numerically by use of the fourth-order Runge–Kutta method. Results are reported for the flow and thermal fields in the melt region. The melting phenomenon decreases the local Nusselt number at the solid–liquid interface.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Transport in porous media 36 (1999), S. 307-339 
    ISSN: 1573-1634
    Schlagwort(e): dispersion ; chromatography ; porous media ; adsorption ; homogenization ; multiple scales expansions.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract This paper is devoted to the computation of effective equations for the transport of a solute in a chromatograph. We focus our attention on models that retain dispersion effects. A chromatograph is a biporous periodic heterogeneous medium, made up of macropores, and of small porous adsorbing crystals that have a retention effect on the solute. We use the method of multiple scales expansions. Various macroscopic behaviours appear, according to the respective orders of magnitude of the dimensionless characteristic parameters: Peclet number in the macropores, ratio of the characteristic time of diffusion in the macropores to the characteristic time of diffusion in the crystals, adsorption coefficient. Dispersion occurs for a Peclet number of order ε−1. We then discuss the effective behaviour of the solute, with respect to the orders of magnitude of the other characteristic parameters. To our knowledge, most of the models are new. Our modelling is not restricted to chromatographs. It applies to various situations of physic and chemical engineering: fixed bed reactors, catalytic cracking, ground water for instance.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Annals of biomedical engineering 26 (1998), S. 850-858 
    ISSN: 1573-9686
    Schlagwort(e): Biomechanics ; Jejunum ; Preconditioning ; Pressure–volume relation ; Stiffness ; Strain softening ; Viscoelasticity ; Mechanics ; Small intestine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Measurement of pressure–volume relations is a commonly used technique to elucidate small intestinal stiffness. There is a lack of data on the relation between stiffness and history-dependent mechanical properties of the gastrointestinal tract. We aimed to distinguish between passive properties of the tissue that depend on the time-history of load (viscoelastic effects) versus those that depend on the maximum previous load (strain softening effects). Ten repeated pressure–volume relations were measured at each peak pressure level in six isolated, passive guinea-pig jejuni in vitro during balloon inflation and deflation cycles. With inflation to a new higher peak pressure (ranging from 3 to 15 mm Hg), the pressure–volume relation became less stiff, particularly in the low pressure range, without a significant change in unloaded jejunal volume. We computed the jejunal normalized volume change as a function of the integrated volume–time history and maximum volume. Analysis of covariance revealed significant dependence of the normalized volume change on the volume–time history (P 〈; 0.001) and the maximum volume history (P 〈; 0.001). Multiple linear regression analysis showed that approximately 90% of the history dependence could be attributed to the maximum volume. Most softening (loss of stiffness) happens in the low pressure range of the curve (0–3 mm Hg). We adopted the Johnson and Beatty strain softening theory and computed the volume amplification factor. This factor was shown to be a linear function of the normalized peak volume (r2 〉 0.999). Since strain softening effects were significantly greater than viscoelastic effects, we conclude that history-dependent changes in jejunal stiffness are more likely to involve alterations to elastic rather than viscous structures in the tissue. These effects must be taken into account when performing balloon distension studies in the gastrointestinal tract for studying physiological and pathophysiological problems in which loading conditions are altered, e.g., mechanoreceptor studies in normal intestine and in acute and chronic obstruction, in order to have an accurate description of the biomechanics. © 1998 Biomedical Engineering Society. PAC98: 8745Bp
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 17
    ISSN: 1573-9686
    Schlagwort(e): Diagnosis ; Rheumatoid arthritis ; Quantitative assessment ; Rheumatology ; Biomechanics ; Patofemoral joint ; Acceleration measurement ; Tibiofemoral joint ; Osteoarthritis ; Vibration arthroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Devising techniques and instrumentation for early detection of knee arthritis and chondromalacia presents a challenge in the domain of biomedical engineering. The purpose of the present investigation was to characterize normal knees and knees affected by osteoarthritis, rheumatoid arthritis, and chondromalacia using a set of noninvasive acceleration measurements. Ultraminiature accelerometers were placed on the skin over the patella in four groups of subjects, and acceleration measurements were obtained during leg rotation. Acceleration measurements were significantly different in the four groups of subjects in the time and frequency domains. Power spectral analysis revealed that the average power was significantly different for these groups over a 100–500 Hz range. Noninvasive acceleration measurements can characterize the normal, arthritis, and chondromalacia knees. However, a study on a larger group of subjects is indicated.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Annals of biomedical engineering 23 (1995), S. 359-374 
    ISSN: 1573-9686
    Schlagwort(e): Neuromuscular ; Muscle mechanics ; Muscle spindle ; Posture ; Movement ; Stability ; Biomechanics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract This paper extends the systematic approach described in Winters and Stark (62) for developing muscle models. The underlying motivation is our finding that for larger scale shoulder and head-neck postural systems to be mechanically stable, open-loop muscle properties are often not sufficient. There are three primary contributions. First, the previous muscle mechanical model structure and parameter estimation process of (62) is updated to reflect recent experimental findings. Second, an intrafusal (IF) muscle model is developed that includes a γ static motoneuron (MN) drive, a Hill muscle model, and a muscle spindle sensor across the IF series element; this provides a more appropriate muscle spindle output signal, especially for studies of posture. Third, the conceptual cut between the neurocontrol input and the actuator is raised from just below the MN summing junction to a higher location, allowing a “musclereflex actuator” to be defined that satisfies the formal theoretical requirement for possessing passive spring-like behavior when the neurocontrol input is constant. α−ψ MN coactivation is assumed, and three types of intrinsic autogenic reflex responses (spindle, Golgi tendon organ, Rhenshaw cell) are developed. Default feedback gains are set based on the criteria that inherent feedback should not sculpt the feedforward excitation drive by more than ±10% of maximum. This new actuator model only mildly affects voluntary goal-directed dynamic performance, but enhances spring-like performance around the postural equilibrium state, in line with available animal and human studies and with several theories on postural regulation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Annals of biomedical engineering 23 (1995), S. 346-358 
    ISSN: 1573-9686
    Schlagwort(e): Saccade ; Extraocular muscles ; Muscle crossbridge models ; Biomechanics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Several phenomenological models of the oculomotor mechanics that produce saccadic eye movements have been developed. These models have been based on measurements of macroscopic muscle and orbital tissue properties and measurements of eye kinematics during saccades. We recorded the forces generated by the medial and lateral recti during saccades in an alert, behaving monkey using chronically implanted force transducers. With this new data, we tested the ability of the classic saccade models to generate realistic muscle force profiles. Errors in the predictions of the classic saccade models led to a reexamination of the current models of extraocular muscle. Both a phenomenological, Hill-type muscle model and an approximation to Huxley's molecular level muscle model based on the crossbridge mechanism of contraction (distribution moment model) were derived and studied for monkey extraocular muscle. Simulations of the distribution moment model led to insights suggesting (i) specific modifications in the lumped force/velocity relationship in the Hill-type model that resulted in this type of phenomenological model being able to generate realistic dynamics in extraocular muscle during saccades; (ii) the distribution of activity in the different fiber types in extraocular muscle may be central to the characteristics exhibited by the muscle during saccades; (iii) the transient properties of lengthening muscle such as yielding are not significant during saccades; and (iv) the series elastic component in active muscle may be predominantly generated by the elastic properties of the cross-bridges.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 20
    ISSN: 1573-9686
    Schlagwort(e): Kinematics ; Kinetics ; Rehabilitation ; Biomechanics ; Generalized center of pressure ; Center of pressure ; Wheelchair propulsion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract The measurement of the center of pressure (COP) has been and continues to be a successful tool for gait analysis. The definition of a similar COP for wheelchair propulsion, however, is not straightforward. Previously, a COP definition similar to that used in force plate analysis had been proposed. Unfortunately, this solution has the disadvantage of requiring a separate COP definition for each plane of analysis. A definition of the generalized center of pressure (GCOP) which is consistent in all planes of analysis is derived here. This definition is based on the placement of a force-moment system, equivalent to the force-moment system at the hub, on a line in space where the moment vector (wrench moment) is parallel to the force vector. The parallel force-moment system is then intersected with three planes defined by anatomical landmarks on the hand. Data were collected using eight subjects at propulsion speeds of 1.34 m/s and 2.24 m/s (1.34 m/s only for subject 1, 0.894 m/s and 1.79 m/s for subject 8). Each subject propelled a wheelchair instrumented with a SMARTWheel. A PEAK 5 video system was used to determine the position of anatomical markers attached to each subject’s upper extremity. The GCOP in the transverse plane of the wrist formed clusters for all subject’s except subject 2 at 1.34 m/s. The clustering of the GCOP indicates that the line of action for the force applied by the hand is approximately perpendicular to the transverse plane through the wrist. When comparing the magnitude of the moment vector part of the wrench with the moment of the force vector of the wrench about the hub, the wrench moment is approximately an order of magnitude smaller. This indicates that the role of the wrist for wheelchair propulsion is primarily to stabilize the force applied by the arm and shoulder. © 1998 Biomedical Engineering Society. PAC98: 8745Dr, 8710+e
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 21
    ISSN: 1573-9686
    Schlagwort(e): Medical imaging ; Magnetic resonance imaging ; Biomechanics ; Tendon moment arm ; Functional neuromuscular stimulation ; Tendon transfer surgery ; Hand biomechanics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract New three-dimensional (3D) magnetic resonance imaging (MRI) methods for measuring the tendon moment arm were created and were evaluated on the tendon moment arm of the flexor digitorum profundus at the third metacarpophalangeal joint. Using an open magnet MRI system and a hand holder, a series of static images were acquired at four joint angles and analyzed using specially created computer programs. Three methods were evaluated: (1) a 3D tendon excursion method that extended the method of Landsmeer; (2) a 3D geometric method whereby the moment arm was the perpendicular distance between the joint axis of rotation and the tendon path, and (3) a two-dimensional (2D) geometric method whereby single image slices were analyzed. Repeating the imaging and measurement processes, the 3D tendon excursion method was more reproducible (6% variation) than the 3D geometric method (12%), and both were much more reproducible than the 2D geometric method (27%). By having three operators analyze a single set of image data, we found that the precision of the 3D tendon excursion method was much less affected by segmentation error than the 3D geometric method. With the 3D imaging methods, tendon bowstringing and a displacement of the joint center of rotation toward the dorsal side of the hand were evident, leading to as much as a 60% increase in moment arm with joint flexion. Because of the dependence on flexion and variation between subjects, we recommend patient-specific measurements for target applications in functional neuromuscular stimulation interventions and tendon transfer surgery. © 1999 Biomedical Engineering Society. PAC99: 8761Pk, 8719Rr, 0705Pj
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Journal of engineering mathematics 33 (1998), S. 103-112 
    ISSN: 1573-2703
    Schlagwort(e): creeping flow ; Brinkman's equation ; porous media ; array of spheres
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Abstract Creeping flow through an array of spheres with small volume fraction φ is studied theoretically. It is observed that it can be described macroscopically by Brinkman's equation. A generalized version of the reciprocity relations is used to determine the viscous term up to O(φ2) for the case of random configuration and up to O(φ3) for the case of periodic, cubic configurations of the fixed bed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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